doc: update testpmd commands for flow director
doc: update testpmd commands for flow director

Because of the changing of unified flow type, commands for flow
director need to be updated.

Signed-off-by: Jingjing Wu <64d28b617c3b4840f5ded1bfa611cba7fadfe5c7@intel.com>

john-mcnamara-intel/dpdk,msune/dpdk,mixja/dpdk,john-mcnamara-intel/dpdk,tsphillips/dpdk-fork,mixja/dpdk,tsphillips/dpdk-fork,mixja/dpdk,venkynv/dpdk-mirror,mixja/dpdk,venkynv/dpdk-mirror,tsphillips/dpdk-fork,john-mcnamara-intel/dpdk,msune/dpdk,msune/dpdk,tsphillips/dpdk-fork,venkynv/dpdk-mirror,msune/dpdk,john-mcnamara-intel/dpdk,venkynv/dpdk-mirror